The present invention relates to a method for molding a ceramic port liner used to line an exhaust port such as a head port and manifold in a gasoline engine or a diesel engine.
In recent years, environmental pollution by automobile exhaust gas has become a serious social problem. Although a measure to eliminate the harmful materials contained in the gas using a catalyst is commonly used, it is desired to reduce the use of noble metals such as Pt and Rh, which are used as a catalyst, from the view point of resource and cost. Moreover, four-valve engines increasing in recent years have the problem of deterioration in a purifying property by a catalyst caused by dropping of the exhaust gas temperature. To solve such problems, it is proposed to raise the exhaust gas temperature by adiabatic function of a ceramic port liner with which the exhaust port of the engine is lined. A ceramic port liner in the present invention is produced by drain casting generally with a gypsum mold or the like. FIGS. 1 and 2 shows a port liner in a forked shape comprising two ports, Port 3a and Port 3b, and an exhaust exit 4 and having two exhaust galleys 2 therein. This type of ceramic port liner has a tendency to be thin at the point of bifurcation 5, where a damage may be often caused.
Pressurized casting has been conventionally known as slip casting and has been adopted mainly for use in solid slip casting. However, it has rarely been applied to drain casting, especially to a fork shaped ceramic port liner. Therefore, matters such as the proper pressure upon molding a ceramic port liner have scarcely been investigated.